Method of producing magnetic cores by using electron irradiation



o ct. 4, 1966 /TTORNEY I AGENT United States Patent O METHOD VOF PRODUCING MAGNETIC -CORES BY USING -ELECTRON IRRADIATION Robert S. Sery, Silver Spring, and Daniel I. Gordon,Chevy Chase, Md., .assignors to the United `States of America as represented by the Secretary of the Navy Filed Apr. 28', 1964, Ser. No. 363,310 Claims. (Cl. 148-100) The invention described herein may be manufactu-red and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties .thereon or therefor.

The present Vinvention relates rto 'the method of treating materials of high magnetic permeability in such a way as to impart to said materials the `characteristic of exhibiting a tri-stable hysteresis loop.

Magnetic materials have extensive use in present day technology, and in some applications such as computer logic circuitry where three memory -states vare needed, for example, it is desirable that these magnetic materials exhibit the characteristic of having tri-stable hysteresis loops. In the past, the only processes known for imparting such characteristics to a magnetic material have been high temperature annealing processes, which require that the magnetic material be subjected to temperatures in the order of 490 C. to 1000 C. for periods vof time exceeding 20 hours. Unlike the prior methods which were extremely cumbersome and time consuming, the present invention prod-uces magnetic materials having tristable hysteresis loops by intermittently irradiating the 'material with electrons while maintaining the ltemperature 'below those conventionally used Ifor thermal annealing.

It is an object of this invention to provide a new method of trea-ting materials of high magnetic permeability to cause the materials to exhibit tri-stable hysteresis loops.

Another object of the invention is to provide a safe, fast, and reliable method of treating materials of high magnetic permeability to exhibit hysteresis loops which have three levels of stability.

The figure of the drawing illustrates a graph which shows the 'hysteresis loops of a particular material both before and after being treated according to the method of the present invention.

In the practice of this invention, 'flat core materials are irradiated with electrons from a suitable electron source, such as a Van de Graaf accelerator, for example, while maintaining the temperature of the core materials generally low with respect to the ordering temperature of the material, i.e. maintaining the temperature of the material below that temperature at which permanent heat treatments are produced. The irradiation of the core material is administered in three separate intermittent stages or doses, each dose 'being separated by an interval of time during which no irradiation is directed upon the core material. 'It has been found that an electron beam having a sufliciently high energy level will, when directed upon a .flat core material, alter the magnetic properties of said material. As a result of this process, it is believed that certain of the atoms in the molecular lattice of the core material are displaced from their normal positions when bombarded by electrons, thus producing interstitial atoms and vacancies, which thereby change the ordering of the material and impart to the material different magnetic characteristics, as evidenced by a change in the shape of its hysteresis loop. 'It is believed that an electron beam as low as 0.5 m.e.v. will produce this eifect and it has been found, for example, that electrons at 2 m.e.v. will defini'tely be sutficient to produce said effect.

By way of example, a punched ring of 4.75% Mo Permalloy (4.75 molybdenum, 79% nickel, and 16.25%

bce

iron) was treated according to the method of this invention in the following manner:

A punched ring of 4.75 Mo Permalloy which had 'been heat treated for lhigh permeability and having an inner diameter of 5/8 inch and an 'outer 'diameter lof 1%; inch and being .006 inch in thickness was irradiated with a 2 m.e.v. electron beam. A AVan de Graaf accelerator was used as the electron source 'and the ring was supported 'by an electrically conductive block which was electrically grounded to serve as an electron collector during the irradiation. The block had internal passages formed therein to permit the flow of a coolant therethrough and thus provided means to maintain the teniperature of the ring material substantially below 'its ordering temperature. The ring or core material was irradiated with the electron beam for a period of 15 minutes, the Van de Graaf accelerator was then shut down for a period of 15 minutes, the core material was again irradiated by the electron beam for a second period of 15 minutes, followed by a second shut down period of 20 minutes duration. `The Van de Graaf accelerator was then reactivated 'for an additional period of 65 minutes, thus completing the treatment. 'During this process, the temperature of the core material ranged from C. at the beginning of the irradiation to a high of 1'34" C. at the end of the irradiation. The electron flux was u e/cm.2 1.13 X 10 -min and the total or integrated electron 'flux was 1.1 1017 electrons/cm.2.

Referring to the figure of the drawings, wherein the hysteresis loop for the ring measured prior to the treatment in the matter of the present invention is shown in dotted line form while the ring's hysteresis loop measured after said treatment is shown in solid line form, it may clearly be 'seen that the magnetic properties of the core material have been appreciably altered by the method of this invention and that Ithe material now exhibits a hysteresis loop which has three distinct levels of stability, i.e. three distinct levels of magnetic induction. The number of doses or periods of irradiation a-re not determinative of the number of saturation levels exhibited by the core materialg' but rather, only one additional saturation level is induced in the material when said material is intermittently irradiated by an electron beam of proper dose and sufiicient energy. The method of the present invention therefore clearly alters the conventional shape of the lhysteresis loop of 'the core material and its magnetic characteristics and renders that material idea'lly suitable for certain applications wherein tri-stable core materials are needed in modern ferro-resonant circuits.

The method described a'bove is intended to be no more than an example and is not intended to restrict the invention to the values and ranges specified. Some of the factors which may selectively vary to change the resultant characteristics of the cores treated according to the method of this invention are the energy level of the electron beam, the current of 'the electron beam, the total integrated electron flux, the temperatures of the core materials, the core materia-l, the dimensions of the core materials, the type of atomic particles used to bombard the core material, and the time durations of irradiation and time durations of rest.

The above method quickly, reliably, and safely produces magnetic cores which are not radioactive and which have tri-stable hysteresis loops from conventional magnetic materials having high magnetic permeability.

'Obviously many modifications and variations of the present invention are possible in light of the above teachings. 'It is therefore to be understood that within the lmaterial comprising the steps of ``interrnittently directing a beam of high energy atomic particles onto the material for collision therewith for predetermined durations of time,

- whereby the number of levels of magnetic sta'bility is increased.

'2.1|A method of treating a material having a high magnetic perrneability to cause the material to exhibit a tristable hysteresis loop comprising the steps of irradiating the material With a beam of electrons of energies greater than 0.5 m.e.v. for la plurality of intermittent predetermined intervals of time, the successive intervals 'being separated by predetermined periods of time during which the material is protected b, from the electrons.

` 3.A method of treating a material of highmagnetic permeability to cause the material to exhibit a tri-stable hysteresis loop comprising the steps of directing an intermittent beam of electrons of energies in excess of 0.5 m.e.v. onto a material of high magnetic permeability, and

` Cooling the material to maintain the temperature of the material below its conventional heat treatment temperature.

4. ;A method of treating a flat core of a nickel-iron alloy having high lmagnetic permeability comprising the steps of irradiating the core with an intermittent beam of high energy atomic particles having an energy level greater than 0.5 m.e.v. for a plurality of predetermined periods of time,

protecting the core from irradiation for preselected intervals of time between said periods of irr'adiation,l and cooling. the core during the periods of irradiation to maintain the temperature of the core below 250 C.,

whereby the core is caused to exhibit a tri-stable hysteresis loop. '5. A method of changing lthe magnetic properties of a nickel-iron alloy of high magnetic permea'bility comprising the steps of irradiating the alloy with an electron beam of an energy level of approximately32 m.e.v. for approximately 'fifteen minutes, i

protecting the a'lloy from irradiation for approximately fifteen minutes,

irradiating the alloy with the electron 'beamfor approxi- I References Cited by the Examiner UNITED STATES PATENTS 1/1961 Steigerwald 148-15 `6/1965 Gordon'et al. 148-100 OTHER REFERENCES Gordon et al.: Article in Solid State Physics in Electronics and Telecommun-ications, vol. .4, pp. 8244858, Sept. 1, 1960.

Seitz et al.: Article in Solid State Physics, vol. 2,V pp. 305-448, June 1956.

Sery et al.: Article in Journal of 'Applied Physics, vol. 34, pp. 1311-1312, April 1963.

DAVID L. RECK, Primary Exam iner. i

N. F. MARKVA,'Assistant Examiner. 

2. A METHOD OF TREATING A MATERIAL HAVING A HIGH MAGNETIC PERMEABILITY OF CAUSE THE MATERIAL TO EXHIBIT A TRISTABLE HYSTERESIS LOOP COMPRISING THE STEPS OF IRRADIATING THE MATERIAL WITH A BEAM OF ELECTRONS OF ENERGIES GREATER THAN 0.5 M.E.V. FOR A PLURALITY OF INTERMITTENT PREDETERMINED INTERVALS OF TIME, THE SUCCESSIVE INTERVALS BEING SEPARATED BY PREDETERMINED PERIODS OF TIME DURING WHICH THE MATERIAL IS PROTECTED FROM THE ELECTRONS. 